Sheets that are not attached in some way to a mattress tend to dislocate. To prevent dislocation, attachable sheets have been developed. Such sheets can generally be divided into two classes depending on whether their use requires modification of the bed on which they are used, possibly by modifying the mattress, bed frame and/or spring box.
The first class includes sheets having fastening members which will operate correctly without modifying the bed and, when removed from the bed, leave no fastening members or portions thereof on the bed. For example, U.S. Pat. No. 5,628,077 to Brigenti discloses the use of drawstrings, U.S. Pat. No. 5,815,861 to Lairange et al. shows T-type or spider net-type elastic fasteners spanning across the bottom of the mattress, and in U.S. Pat. No. 5,179,743 to Lanman, long elastic straps diagonally extending across the bottom of the mattress are used. Another example is U.S. Pat. No. 4,937,904 to Ross wherein elastic bands, slideably connected through openings in the sheet, are used to help prevent dislocation of the sheet. Sheets from this class generally cooperate well with many different mattresses, but their use tends to be problematic in that they generally require the mattress to be turned over or otherwise moved for installation and/or adjustment of the sheet fasteners.
The second class includes sheets having fasteners that will not operate correctly without modifying the bed, and when removed from the bed, leave a fastening member or portion thereof on the bed. Such fasteners generally comprise at least two portions that can be coupled together. One portion is connected to the bed, the other to the sheet, and the two portions are coupled together when the sheet is placed on the bed and uncoupled when the sheet is removed from the bed. Examples of such fasteners include buckles, zippers, snaps or hook and loop type fasteners. As used herein, a "fastener" is often an assembly of elements such as a buckle with a pair or elastic or adjustable straps with one strap permanently connected to the side of the mattress, and the other strap permanently connected to the sheet. Another example is found in U.S. Pat. No. 4,698,880 to Hamm, in which a wedge connected to the bed frame contacts the sheet and an additional element holds the wedge and sheet together in a fixed position.
Sheets in the second class can generally be put on and taken off of a bed with little or no movement of the mattress. However, their use requires modification of the mattress by attaching a portion of each of the sheet fasteners to the bed. If one purchases a mattress having permanently installed fastener elements, one's choice in purchasing sheets is limited to those choices which have fastener elements of the same type as found on the mattress. Moreover, in facilities having a large number of beds such as a hospital, using attachable sheets becomes more burdensome if different beds have different types of fasteners (even if not permanently installed) because of the need to match particular sheets to particular beds. Although one could utilize a standard fastener type on all beds, doing so tends to be costly as choices for new or replacement beds is limited by fastener type, and switching to a new fastener type requires modifying every bed in the facility.
As the use of known attachable sheets tends to be problematic, there is a continuing need to develop improved bed assemblies which include attachable sheets.